The Tianma 65 m radio telescope antenna

The Tianma 65 m radio telescope(TMRT)at Shanghai is a fully steerable single-dish radio telescope in China,operating at centimeter to millimeter wavelengths(1.25 GHz to 50 GHz).This paper presents details on the main specifications,design,performance analysis,testing,and construction of the telescope antenna.The measured total efficiency is better than 50%over the whole elevation angle range,first sidelobe levels are less than−20 dB,antenna system noise temperatures are less than 70 K at 30°elevation angle,and pointing accuracy is less than 3″.The measured and calculated results are in good agreement,verifying the effectiveness of the design and analysis.

The Tianma 65 m radio telescope at Shanghai

The Shanghai Tianma 65 m radio telescope(TMRT)is a large,fully rotatable radio telescope with multiple scientific purposes.The main body of the telescope and four low-frequency receiving systems,including L,C,and S/X bands,were completed between 2008 and 2012.From 2013 to 2017,four high-frequency receiving systems,including Ku,K,Ka,and Q bands,were constructed and their performance was comprehensively tested.There are three main innovations.(1)A fully movable large radio telescope system with advanced performance and complete functions has been built.(2)An advanced,reliable main reflector adjustment system has been completed,overcoming gravity deformation and creating a large antenna with a main reflective surface accuracy of 0.28 mm(root mean square)for any elevation.(3)Five innovative technologies have been developed to achieve high-precision pointing in any direction within 3″.The TMRT has made a crucial contribution to the orbital measurement and positioning of China’s lunar and deep space probes.Significantly enhancing China's ability to participate in international VLBI observations and radio astronomy,this has facilitated a series of achievements in observational radio astronomical research,in areas such as VLBI,spectral lines,and pulsars.

Surface shape detection methods for large radio telescopes

The surface accuracy of a radio telescope is directly related to its operational efficiency and detection sensitivity.This is crucial under high-frequency observation conditions,where surface shape errors need to be controlled to within 1/16 of the working wavelength.In addition,the primary reflector of large radio telescopes is subject to dynamic deformation,caused by factors such as gravity and thermal effects.This paper presents a method for detecting the surface shape of radio telescopes using radio interferometry techniques combined with active reflector adjustment technology.This enables accurate assessment and correction of surface errors,ensuring the electrical performance of the radio telescope.This study investigates the practical applications of high-precision measurement techniques,such as microwave holography,out-of-focus holography,and wavefront distortion methods at the Tianma 65 m radio telescope(TMRT).Furthermore,the study presents the construction method of gravity models at different elevation angles and demonstrates the efficacy of the active reflector model.The results of the measurements indicate that the application of these methods to the TMRT has led to a notable enhancement of the accuracy of the primary reflector and a substantial improvement in efficiency in the Q-band.Through a process of iterative measurements and adjustments,the surface shape error is ultimately reduced to 0.28 mm root mean square(RMS).

Terrain-influenced wind flow of the Qitai radio telescope site

The wind environment of a site is one of the important factors affecting the observation performance of large aperture and high-performance radio telescopes.Exploring the relationship between the effects of different terrains on wind flow is important to optimize the wind environment of the site.The terrain of the Qitai radio telescope(QTT)site located in east Tianshan Mountains at an elevation of about 1800 m was used to study the wind flow in the adjacent zone of antenna based on numerical simulation.The area from 600m south to 600m north of the antenna is defined as the antenna adjacent zone,and three groups of boundaries with different terrains are set up upstream and downstream,respectively.Since the zone where the antenna is located is a slope terrain,in order to verify the influence of terrain on the wind flow and to clarify the relationship between the influence of boundary terrain on the wind flow,a control group of horizontal terrain is constructed.The simulation results show that the wind flow is mainly influenced by the terrain.The highest elevation of the upstream and downstream boundary terrains affects the basic wind speed.The upstream boundary terrain has a greater impact on wind flow than the downstream boundary terrain.In addition,the wind speed profile index obtained by numerical simulation is smaller than the actual index for the wind from south.Therefore,the wind speed at the upper level(about 100 m)obtained by inversion based on the measured wind speed at the bottom(about 10 m)is also smaller than the actual wind speed.

VLBI observations with the Kunming 40-meter radio telescope

The Kunming 40-meter radio telescope is situated in the yard of the Yunnan Astronomical Observatory （Longitude： 102.8° East, Latitude： 25.0° North） and saw its first light in 2006 May. The Kunming station successfully joined the VLBI tracking of China＇s first lunar probe ＂Chang＇E-1＂ together with the other Chinese telescopes： the Beijing Miyun 50-meter radio telescope, Urumqi Nanshan 25-meter radio telescope, and Shanghai Sheshan 25-meter radio telescope, and received the downlinked scientific data together with the Miyun station from October of 2007 to March of 2009. We give an introduction to the new Chinese VLBI facility and investigate its potential applications. Due to its location, the Kunming station can significantly improve the u - v coverage of the European VLBI Network （EVN）, in particular, in long baseline observations. We also report the results of the first EVN fringe-test experiment of N09SX1 with the Kunming station. The first fringes in the European telescopes were successfully detected at 2.3 GHz with the ftp-transferred data on 2009 June 17. From scheduling the observations to performing the post correlations, the Kunming station shows its good compatibility to work with the EVN. The imaging result of the extended source 1156＋295 further demonstrates that the Kunming station greatly enhances the EVN performance.

Pulsar timing observations with Haoping Radio Telescope

We report pulsar timing observations carried out in L-band with NTSC’s 40-meter Haoping Radio Telescope(HRT),which was constructed in 2014.These observations were carried out using the pulsar machine we developed.Timing observations toward millisecond pulsar J0437–4715 obtain a timing residual(r.m.s.)of 397 ns in the time span of 284 days.Our observations successfully detected Crab pulsar’s glitch that happened on 2019 July 23.

Active sub-reflector research for a large radio telescope

This paper proposes an active sub-reflector suitable for large radio telescopes,which can compensate both of the deformation of the main reflector and sub-reflector position offsets.The mathematical formula of the main reflector deformation compensated by the sub-reflector is deduced based on Cassegrain and Gregory antenna structures.The position of the sub-reflector is adjustable to compensate for defocusing errors on high and low elevations,which are mainly caused by the deformation of the sub-reflector supporting legs.In this paper,the method of obtaining the optimum position of the sub-reflector from the aperture phase by the interferometric method is introduced.The actual measurement is verified on the Tianma 65 m radio telescope,which provides a new way to diagnose the position error of the sub-reflector.

Research on actuator distribution and panels for a radio telescope

Trying to achieve the best surface accuracy control with the fewest actuators, this article mainly studies the distribution of actuators and the method of panel design. The influence of the number of faulty actuators on the accuracy of the surface shape is demonstrated. In addition, the method incorporating a triangular panel, node index and the fitting solution method of a single panel is also given. This method provides a reference for the design and realization of an active surface or a deformable sub-reflector for high performance large aperture radio telescopes.

Error analysis and distribution of the driving mechanism for large spherical radio telescope active reflector

In order to reduce the cost,3-PRS mechanism is introduced into the application of supporting theactive reflector unit of large radio telescope.The kinematic model of 3-PRS mechanism with rotationaljoint errors is derived to solve the error problem in actual engineering application.Then based on the errormodel,inverse and forward kinematics are analyzed.Because the solutions can not be analytically ex-pressed,a numerical method is applied.Afterwards,the parasitic motion errors are analyzed using searchmethod and empirical formulas of the maximum parasitic motion error are put forward.Finally,the toler-ance is distributed using empirical formulas to avoid interference between adjacent reflector units.Theanalyses provide a theoretical basis for the design and installation of large radio telescope active reflector.

Analyzing the capability of a radio telescope in a bistatic space debris observation system

A bistatic space debris observation system using a radio telescope as the receiving part is introduced. The detection capability of the system at different working frequencies is analyzed based on real instruments. The detection range of targets with a fixed radar cross section and the detection ability of small space debris at a fixed range are discussed. The simulations of this particular observation system at different transmitting powers are also implemented and the detection capability is discussed. The simulated results approximately match the actual experiments. The analysis in this paper provides a theoretical basis for developing a space debris observation system that can be built in China.

A study of the strong pulses detected from PSR B0656+14 using the Urumqi 25-m radio telescope at 1540 MHz

We report on the properties of strong pulses from PSR B0656＋14 by analyzing the data obtained using the Urumqi 25-m radio telescope at 1540 MHz from August 2007 to September 2010.In 44 h of observational data,a total of 67 pulses with signal-to-noise ratios above a 5σthreshold were detected.The peak flux densities of these pulses are 58 to 194 times that of the average profile,and their pulse energies are 3 to 68 times that of the average pulse.These pulses are clustered around phases about 5-ahead of the peak of the average profile.Compared with the width of the average profile,they are relatively narrow,with the full widths at half-maximum ranging from 0.28 ° to 1.78 °.The distribution of pulse-energies follows a lognormal distribution.These sporadic strong pulses detected from PSR B0656＋14 have different characteristics from both typical giant pulses and its regular pulses.

Non-uniform temperature distribution of the main reflector of a large radio telescope under solar radiation

The non-uniform temperature distribution of the main reflector of a large radio telescope may cause serious deformation of the main reflector,which will dramatically reduce the aperture efficiency of a radio telescope.To study the non-uniform temperature field of the main reflector of a large radio telescope,numerical calculations including thermal environment factors,the coefficients on convection and radiation,and the shadow boundary of the main reflector are first discussed.In addition,the shadow coverage and the non-uniform temperature field of the main reflector of a 70-m radio telescope under solar radiation are simulated by finite element analysis.The simulation results show that the temperature distribution of the main reflector under solar radiation is very uneven,and the maximum of the root mean square temperature is 12.3℃.To verify the simulation results,an optical camera and a thermal imaging camera are used to measure the shadow coverage and the non-uniform temperature distribution of the main reflector on a clear day.At the same time,some temperature sensors are used to measure the temperature at some points close to the main reflector on the backup structure.It has been verified that the simulation and measurement results of the shadow coverage on the main reflector are in good agreement,and the cosine similarity between the simulation and the measurement is above 90%.Despite the inevitable thermal imaging errors caused by large viewing angles,the simulated temperature field is similar to the measured temperature distribution of the main reflector to a large extent.The temperature trend measured at the test points on the backup structure close to the main reflector without direct solar radiation is consistent with the simulated temperature trend of the corresponding points on the main reflector with the solar radiation.It is credible to calculate the temperature field of the main reflector through the finite element method.This work can provide valuable references for studying the thermal deformation and the surface accuracy of the main reflector of a large radio telescope.

EFFECT OF FEED ARRAY CONFIGURATION ON THE FIELD-OF-VIEW OF RADIO TELESCOPE ANTENNA

Phased Array Feed (PAF) is a small two-dimensional phased array antenna, playing a role as the multi-beam feed for the reflector antenna. The prominent capability of large continuous Field-of-View (FoV) coverage and fast survey speed makes PAF the promising feed for radio telescopes. In this paper, the effect of feed array of PAF on the gain fluctuations over FoV is analyzed on a sim- plified model of the Five-hundred-meter Spherical Aperture radio Telescope (FAST), including illu- mination pattern edge taper, element spacing, element arrangement and element amount. And the differences between rectangular and hexagonal array arrangements are compared. The relationship between the FoV and array configuration are concluded at last.

A Millimeter-Wave Radio Telescope Project at Seoul National University

The Department of Astronomy at Seoul National University is carrying out a project to build a radio observatory, the Seoul Radio Astronomical Observatory (SRAO). The observatory will be constructed on our campus, which is located at sea level in Seoul, Korea, at (126°57.′3E, 37°27.′1N). The observatory will operate a 6 m millimeter radio telescope.

Hybrid position/force control strategy and experiment of the six-cable driven parallel manipulator for the forty-meter aperture radio telescope

This paper mainly analyzes a hybrid position/force control strategy and experiment of a six-cable driven parallel manipulator for a forty-meter aperture radio telescope. Through the establishments of a kinematic model, a catenary model and a cable-force characteristics model, a basic method is presented based on preventing the pseudo-drag problem of a flexible cable and realizing the hybrid position/force control for a six-cable driven parallel manipulator, and a hybrid position/force control system is developed. Some specific experiments in two typical velocities for astronomical observations are carried out. Experimental results show that the tracking accuracy is related to the speed of the movement. The desired tracking accuracy of the support system is achieved through an effective hybrid position/force control strategy, the cable forces are controlled effectively, and the pseudo-drag problem of flexible cable is solved. This study establishes the foundation of achieving the harmonious movement of the six-cable driven parallel manipulator, A-B rotating platform and the Stewart fine tuninz olatform.

A Study of the Fitting Accuracy of the Active Reflector for a Large Spherical Radio Telescope

We propose a spatial three-degree-of-freedom (DOF) parallel mechanism combining two degrees of rotations and one degree of translation to support the active reflector units of a large spherical radio telescope. The kinematics, workspace and accuracy of the mechanism are analyzed. One-dimensional and two-dimensional fitting errors to the working region of active reflector are investigated. Dimensional parameters of the mechanism and active reflector unit are examined with respect to the requirement of fitting accuracy. The result of accuracy analysis shows the effectiveness and feasibility of the proposed mechanism, and gives a design rule to guarantee the highest working frequency required by large radio telescope.

Construction Finishes on World's Largest Single Dish Radio Telescope

After more than five years of construction,the world’s biggest single-dish radio telescope was finally ready to open its eye.On September 25,2016,the Fivehundred-meter Aperture Spherical radio Telescope(FAST)was officially put into use in a mountainous region of southwest China's Guizhou Province.With a total collecting area equivalent to the size of 30 soccer fields,FAST is expected to accomplish large scale

Man behind World's Largest Radio Telescope Passes Away at 72

NAN Rendong,a distinguished expert in radio astronomy who is known as the father of the world’s largest radio telescope,died from lung cancer in Boston on September 15,2017 at the age of 72.His untimely passing away was just ten days before his masterpiece,the Five-hundred-meter Aperture Spherical radio Telescope(FAST),which he spent over two decades conceiving and building for the next generation

IPS observation system for the Miyun 50m radio telescope and its commissioning observation

Ground-based observation of Interplanetary Scintillation （IPS） is an impor- tant approach for monitoring solar wind. A ground-based IPS observation system has been newly implemented on a 50 m radio telescope at Miyun station, managed by the National Astronomical Observatories, Chinese Academy of Sciences. This observa- tion system has been constructed for the purpose of observing solar wind speed and the associated scintillation index by using the normalized cross-spectrum of a simul- taneous dual-frequency IPS measurement. The system consists of a universal dual- frequency front-end and a dual-channel multi-function back-end specially designed for IPS. After careful calibration and testing, IPS observations on source 3C 273B and 3C 279 have been successfully carried out. The preliminary observation results show that this newly-developed observation system is capable of performing IPS observa- tion. The system＇s sensitivity for IPS observation can reach over 0.3 Jy in terms of an IPS polarization correlator with 4 MHz bandwidth and 2 s integration time.

The Qitai radio telescope

This study presents a general outline of the Qitai radio telescope(QTT)project.Qitai,the site of the telescope,is a county of Xinjiang Uygur Autonomous Region of China,located in the east Tianshan Mountains at an elevation of about 1800 m.The QTT is a fully steerable,Gregorian-type telescope with a standard parabolic main reflector of 110 m diameter.The QTT has adopted an umbrella support,homology-symmetric lightweight design.The main reflector is active so that the deformation caused by gravity can be corrected.The structural design aims to ultimately allow high-sensitivity observations from 150 MHz up to115 GHz.To satisfy the requirements for early scientific goals,the QTTwill be equipped with ultra-wideband receivers and large field-of-view multi-beam receivers.A multi-function signal-processing system based on RFSo C and GPU processor chips will be developed.These will enable the QTT to operate in pulsar,spectral line,continuum and Very Long Baseline Interferometer(VLBI)observing modes.Electromagnetic compatibility(EMC)and radio frequency interference(RFI)control techniques are adopted throughout the system design.The QTT will form a world-class observational platform for the detection of lowfrequency(nano Hertz)gravitational waves through pulsar timing array(PTA)techniques,pulsar surveys,the discovery of binary black-hole systems,and exploring dark matter and the origin of life in the universe.The QTT will also play an important role in improving the Chinese and international VLBI networks,allowing high-sensitivity and high-resolution observations of the nuclei of distant galaxies and gravitational lensing systems.Deep astrometric observations will also contribute to improving the accuracy of the celestial reference frame.Potentially,the QTT will be able to support future space activities such as planetary exploration in the solar system and to contribute to the search for extraterrestrial intelligence.